FISH ADAPTATION

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CHAPTER 3 FISH ADAPTATION
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• 1. ADAPTATION AND HOMEOSTASIS
• morphology, physiology and behaviour of an animal
  are very well matched to survive in its
  environment adaptation
• acclimatization physiological change within an
  individual animal resulting from new
  environmental conditions
• - homeostasis tendency of organisms to maintain
  relative internal stability

Walter B. Cannon (1871-1945)
Claude Bernard (1813-1878)
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• homeostasis is accomplished via feedback
  mechanisms

sensor
detected by
afferent pathway
control centre
inbalance
balance
e.g. brain
efferent pathway
restores
effector
e.g. muscles, glands, ...
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• conformers vs. regulators

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• fish select temperatures at which they maximize
  various functions
• Example sockeye salmon select an ambient
  temperature of 15C at which feeding rate,
  digestive rate, active metabolism, cardiac work,
  growth rate, and sustained swimming velocity are
  maximized. With the cessation of feeding, young
  sockeyes selected colder temperatures, thereby
  reducing the cost of maintenance.

sockeye salmon (Oncorhynchus nerka)
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1.2. Adaptation to salinity variation (
osmoregulation)
dg/L
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• Osmoconformers animals that conform to the
  osmolarity of the environment, e.g. marine
  elasmobranchs, coelacanth, crab-eating frog,
  various marine invertebrates
• Osmoregulators animals that maintain an
  internal osmolarity different from the
  environment most vertebrates (including
  teleosts) are strict osmoregulators
• Osmoregulation biological processes involved in
  the maintenance of the osmolarity of body fluids
  within the range of physiological tolerance of
  the species
• - maintaining solute (salt) concentration in body
  fluids
• - maintaining water balance in body
• gills, kidneys and intestine are main
  osmoregulatory organs
• (? See Physiology of Aquatic Organisms)

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- stenohaline fish tolerate a narrow range of
salinities - most marine fish and freshwater
fish - euryhaline fish tolerate a wide range of
salinities - estuary, tidal zones, salt marches
(e.g. killifish) - diadromous (migrating)
fish - anadromous FW?SW?FW (e.g. salmon) -
catadromous SW?FW?SW (e.g. eel)
mummichog (Fundulus heteroclitus)
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• 2. STRESS
• stress the physiological resultant of demands
  that exceed an organisms regulatory capacities
• stressor environmental factor causing stress in
  the organism
• acute stress stress of short duration (minutes
  to hours), e.g. netting, grading, handling,
  vaccination, hauling,
• chronic stress continuous forms of stress (days
  to weeks), e.g. overcrowding, variable water
  quality, social domination, exposure to novel
  environments,
•  general adaptation syndrome  (Selye, 1946)
  (1) alarm, (2) adaptation, (3) exhaustion
• response to stressors is a vitally important
  normal response allowing the organism to avoid or
  cope with challenges to homeostasis!
• stress responses behavioural, physiological,
  cellular

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• 2.1. Behavioural responses to stress
• alterations in behaviour like food acquisition,
  predator avoidance, migration, habitat preference
  ? avoiding or mitigating exposure to the stressor
  and minimizing energetic demand
• minutes to weeks te return to pre-stress
  conditions, depending on nature and magnitude of
  stressor
• if avoidance or behavioural mitigation is not
  possible, induced changes in behaviour may then
  reflect deleterious changes in how an animal
  senses and responds to its environment
• behavioural and physiological responses to a
  stressor are intimately related

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The alteration of school behavioural parameters
(CZ, SDZ) in Nile tilapia under different ammonia
concentrations. All parameters are given out
every 2 min. A Under low ammonia level B Under
moderate level C Under high level (CZ is the
mean location of the school in Z direction SDZ
indicates the average dimension or density of the
school) (from Xu et al., 2005)
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Effects of a 24- (A) or 72-h (B) exposure period
to 80 (8.3 mg/l), 50 (5.2 mg/l), or 35 (3.6
mg/l) O2 saturation on food intake in rainbow
trout (n 8). BW, body weight. a,b,cPre-post
differences that do not share a common letter are
significantly different from each other as
determined using one-way ANOVA and pairwise
Tukey's test. Paired Student's t-tests were
carried out between the pre- and postexposure
values for each treatment group, with significant
differences indicated (P lt 0.05). (from Bernier
Craig, 2005)
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• stress-related behavioural (and physiological)
  changes are mediated by CRH-like peptides (CRH,
  UT-I)

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• 2.2. Physiological responses to stress
• primary stress response neuroendocrine response
  ? release of stress hormones catecholamines,
  cortisol

Brain
Hypothalamus
CRH
Sympathetic nerves
Pituitary
ACTH
Chromaffin tissue in headkidney
Interrenal tissue in headkidney
adrenaline noradrenaline
GR
cortisol
Target tissues
AR
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• caution in using indicators of stress resting
  plasma cortisol values differ according to time
  of day and season, age, sex and state of
  maturity, environmental temperature, and
  species/strain of fish!
• secondary stress response biochemical and
  physiological effects associated with stress,
  mediated to a large extent by stress hormones,
  e.g. increased plasma glucose or lactate
  concentrations
• stress hormones switch the fishs metabolism from
  an anabolic state to a catabolic state energy
  mobilization
• stress hormones ? glycogenolysis, gluconeogenesis
  ? plasma glucose? ? energy for brain, gills,
  muscles to cope with increased energy demand

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(a) Plasma cortisol, (b) plasma glucose, and (c)
serum interleukin-10 levels in stressed fish.
Zero time point stands for the control unstressed
group. Time points of 1, 2 and 4 h stand for
groups of fish subjected to single, double and
triple handling stress, respectively. Depicted
are means and standard deviations. (from Dror et
al., 2005)
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• 2.3. Cellular responses to stress
• heat shock proteins (Hsp) or  stress proteins 
  (Hsp90, Hsp70, low molecular weight Hsp)
  expression increases in response to stressors ?
  enhances stress tolerance
• how does the action of Hsp at the molecular level
  lead to whole-organism stress tolerance?????
• development of new molecular tools to study an
  integrated stress response, e.g. DNA microarrays

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medaka (Oryzias latipes)
zebrafish (Danio rerio)
green spotted pufferfish (Tetraodon nigroviridis)
Japanese pufferfish (Takifugu rubripes)
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• 2.4. Consequences of stress for fish production
• tertiary stress response whole-animal and
  population level changes associated with stress
• if the fish is unable to acclimate or adapt to
  the stressor ? decreased growth, reproductive
  capacity, immunity,... cause stress-mediated
  energy repartitioning (energy is diverted away
  from these processes to cope with stress)
• effects of stress on survival
• respiratory stress (due to increased oxygen
  demand)
• osmoregulatory failure stress hormones ? gills
  become leaky for water and ions ?
  osmoregulation becomes more challenging for fish
• decreased disease resistance

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The mean (SE) opercular beat frequency (beats
per minute) of fish from high- and low-predation
sites under normal activity levels in their home
tanks. (from Brown et al., 2005)
Phagocytosis of FITC-labelled Vibrio anguillarum
by head-kidney leucocytes from stressed (crowded)
(grey) and control (undisturbed) (white) gilthead
seabream. (a) Phagocytic ability (b) phagocytic
capacity. Data represent the meanS.E. Asterisks
denote statistically significant differences
(Plt005) between control and stressed groups.
(from Ortuño et al., 2001)
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• effects of stress on growth cessation of feeding
  activity (behavioural stress response)
  catabolic effects of stress hormones
  (physiological stress response) ? growth
  suppression
• effects of stress on reproduction suppression of
  reproductive hormones, reduced gamete viability,
  gonadal growth retardation

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Mean body mass (g) of repeatedly stressed and
unstressed Eurasian perch (a) and rainbow trout
(b) during an 8-week period. Data represent
u  S.E.M., n  3. Means labeled are different
at P lt 0.05.
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Effect of repeated temperature stress on
testicular development. (A) Gonadosomatic index.
Data sharing the same underscores are not
significantly different (n20). (B) Stages of
spermatogenesis at 95 dph. Expressed as the
percentage of animals in the respective treatment
groups in a certain stage of spermatogenesis
(n10). (from Goos Consten, 2002)
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• 2.5. Stress control in aquaculture
• duration of stress response is proportional to
  duration of stress ? reducing time-course of
  netting, grading or hauling will encourage a more
  rapid recovery of the fish
• stress-induced mortality increases with
  increasing water temperature ? undertake netting,
  grading, hauling at lower water temperatures
• effects of multiple stressors may be additive or
  even synergistic ? if repeated stresses are
  unavoidable, allow a sufficient recovery period
  between stresses
• use of dilute salt solutions in FW fish or
  dilution of seawater in SW fish during severe
  stresses have been shown to be effective in
  limiting osmotic stress and reducing
  stress-associated mortality
• withdrawal of food 2-3 days prior to confinement
  prevents fouling of the water reduces oxygen
  requirements and thus respiratory stress

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• anaesthesia can suppress the cortisol response to
  an acute stress such as handling and reduce
  mortality if the fish are subsequently exposed
  without anaesthesia to a second stressor
• in case of species/strains new to cultivation, an
  understanding of the fishs natural habitat can
  provide insight into methods of stress control
• genetic selection for strains with lower
  magnitude of stress response (already taken place
  in rainbow trout domestication)